The present invention relates generally to a computer-generated hologram, and more particularly to a computer-generated hologram suitable for use as a reflector and its fabrication process as well as a reflective liquid crystal display using a computer-generated hologram.
Of a variety of display systems already put to practical use, liquid crystal display systems have now wide applications because they have some advantages of low power consumption, color display capability, low-profile size, and low weight.
Instead of LCDs, it is difficult to use other type of displays for terminal equipment having no other choice to rely on batteries or accumulators.
However, LCDs cannot emit light by themselves; in other words, extraneous light or illumination light is necessary for viewing images irrespective of whether they are of the reflection type or the transmission type.
However, the use of sufficiently bright illumination light goes against the valuable advantage of low power consumption. Accordingly, even when illumination light is used, it is unreasonable to make use of illumination having relatively high illuminance; whether the light used is extraneous light or illumination light, how limited light is effectively used is of vital importance.
The applicant has already filed patent applications (JP-A's 11-296054 and 11-183716) to come up with computer-generated holograms having a phase distribution capable of diffracting obliquely incident light in a predetermined viewing region. Of both, JP-A 11-296054 discloses a computer-generated hologram having a phase distribution for allowing light incident thereon at an oblique angle of incidence to be diffracted into the predetermined viewing region.
To fabricate these computer-generated holograms which are still found to have the desired effects, however, it is required to use a time-consuming, inefficient fabrication process comprising the steps of using a computer to find phase distributions all over the hologram region by computations, and making a relief pattern for the replication of computer-generated holograms on the basis of computation results.
For photoetching in particular, it is preferable to make use of a photomask fabrication system because precise exposure is needed. However, the photomask fabrication system has some disadvantages of high cost, severe fabrication conditions and extended fabrication time, in which the extended fabrication time in particular offers a grave problem.